Method and System for Estimating Life-Expectancy of Secondary Battery

Abstract

It is an object of the present invention to provide a technique for specifically estimating a life expectancy of a secondary battery. The technique performs the steps of: determining an accumulating portion resistance of the secondary battery from an internal resistance thereof; determining an accumulating portion resistance increase coefficient under operating conditions of the secondary battery; and estimating a life expectancy of the secondary battery from the accumulating portion resistance and the accumulating portion resistance increase coefficient.

1 . A method for estimating a life expectancy of a secondary battery, comprising;
 determining an internal resistance of the secondary battery from variations in current and voltage;   determining an accumulating portion resistance of the secondary battery from the internal resistance;   determining an increase coefficient of said accumulating portion resistance from condition parameters including an operating voltage and a surrounding temperature of the secondary battery; and   estimating a life expectancy of the secondary battery from the accumulating portion resistance and the increase coefficient.   
     
     
         2 . The method of  claim 1 ,
 wherein the life expectancy is calculated from a time when variations in current and voltage are obtained.   
     
     
         3 . The method of  claim 1 ,
 wherein the secondary battery is a lithium secondary battery.   
     
     
         4 . The method of  claim 1 ,
 wherein said estimating said life expectancy is based on the following formula:
     R   2     —     max   −R   2     —     now   =R   2     —     0   ·a ·( t     —     max   −t     —     now ) 
   Wherein R 2  is said accumulating portion resistance, R 2     —     max  is a maximum value of the accumulating portion resistance R 2 ,   t   —     max  is a time when the accumulating portion resistance R 2  reaches R 2     —     max ,   t   —     now  is a time when the internal resistance R 1  is determined,   R 2     —     now  is a accumulating portion resistance R 2  at the time t   —     now      a is a increase coefficient of accumulating portion resistance,   R 2     —     0  is an initial value of accumulating portion resistance R 2 .   
     
     
         5 . The method of  claim 1 ,
 wherein said determining an accumulating portion resistance is based on the following formula:   
       
         
           
             
               
                 R 
                 1 
               
               - 
               
                 
                   
                     R 
                     5 
                   
                   · 
                   
                     R 
                     6 
                   
                 
                 
                   
                     R 
                     5 
                   
                   + 
                   
                     R 
                     6 
                   
                 
               
               + 
               
                 
                   1 
                   
                     
                       
                         
                           R 
                           5 
                         
                          
                         
                           R 
                           6 
                         
                       
                       
                         R 
                         2 
                       
                     
                   
                 
                  
                 
                   { 
                   
                     
                       
                         
                           
                             
                               
                                 
                                   R 
                                   5 
                                   2 
                                 
                                  
                                 
                                   R 
                                   6 
                                   2 
                                 
                               
                               
                                 
                                   R 
                                   5 
                                 
                                 + 
                                 
                                   R 
                                   6 
                                 
                               
                             
                              
                             
                               coth 
                                
                               
                                 ( 
                                 
                                   
                                     
                                       
                                         R 
                                         5 
                                       
                                        
                                       
                                         R 
                                         6 
                                       
                                     
                                     
                                       R 
                                       2 
                                     
                                   
                                 
                                 ) 
                               
                             
                           
                           + 
                         
                       
                     
                     
                       
                         
                           
                             
                               
                                 2 
                                  
                                 
                                   R 
                                   5 
                                 
                               
                                
                               
                                 R 
                                 6 
                               
                             
                             
                               
                                 R 
                                 5 
                               
                               + 
                               
                                 R 
                                 6 
                               
                             
                           
                           · 
                           
                             1 
                             
                               sinh 
                                
                               
                                 ( 
                                 
                                   
                                     
                                       
                                         R 
                                         5 
                                       
                                        
                                       
                                         R 
                                         6 
                                       
                                     
                                     
                                       R 
                                       2 
                                     
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                   } 
                 
               
               + 
               
                 R 
                 4 
               
             
           
         
         wherein R 4  is a resistance of electrode non-facing portions of said secondary battery, 
         R 5  is a resistance of a positive-pole current collector of said secondary battery, 
         R 6  is a resistance of a negative-pole current collector of said secondary battery, 
         wherein R 4 , R 5 , and R 6  are design parameters of said secondary battery, and 
         wherein R 4 , R 5 , and R 6  are determined prior to estimating said life expectancy. 
       
     
     
         6 . The method of  claim 1 ,
 wherein determining said internal resistance of the secondary battery is based on resistance of non-facing portions electrode and current collectors.   
     
     
         7 . An apparatus for estimating a life expectancy of a secondary battery, comprising:
 an input/output unit;   an operation unit;   a storage unit; and   an interface unit;   
       wherein said operation unit further comprising; 
       an internal resistance determining unit; 
       an accumulating portion resistance determining unit; 
       an increase coefficient of accumulating portion resistance determining unit; and 
       a life-expectancy estimation unit; 
       wherein said increase coefficient determining unit configured to determine an increase coefficient of accumulating portion resistance by assigning operating condition parameters including an operating temperature and an operating voltage of the secondary battery; 
       and 
       wherein said life-expectancy estimation unit configured to estimate a life expectancy of the secondary battery using said accumulating portion resistance and said increase coefficient of accumulating portion resistance. 
     
     
         8 . The apparatus of  claim 7 , wherein said storage unit prestores an accumulating portion resistance determining function configured to determine an accumulating portion resistance of the secondary battery by assigning an internal resistance of the secondary battery;
 an increase coefficient determining function configured to determine an increase coefficient of accumulating portion resistance by assigning operating condition parameters including an operating temperature and an operating voltage of the secondary battery; and   a life-expectancy estimation function configured to estimate a life expectancy of the secondary battery using the accumulating portion resistance and the accumulating portion resistance increase coefficient.   
     
     
         9 . The apparatus of  claim 8 , wherein the internal resistance determining unit performs processes for:
 accepting a life-expectancy estimation start command for instructing a start of life expectancy estimation and the operating condition parameters from a user via the input/output unit;   receiving current and voltage change values via the interface unit, and holding the current and voltage change values together with the time of reception of these values; and   determining an internal resistance from the held current and voltage change values,   wherein the accumulating portion resistance determining unit performs the steps of:   reading the accumulating portion resistance determining function from the storage unit; and   determining an accumulating portion resistance by assigning the internal resistance determined by the internal resistance determining unit to the read accumulating portion resistance determining function.   
     
     
         10 . The apparatus of  claim 8 , wherein the increase coefficient determining unit performs processes for:
 reading the increase coefficient determining function from the storage unit; and   determining an increase coefficient of accumulating portion resistance by assigning the operating condition parameters received by the internal resistance determining unit to the read increase coefficient determining function.   
     
     
         11 . The apparatus of  claim 8 , wherein the life-expectancy estimation unit performs processes for:
 reading the life-expectancy estimation function from the storage unit; and   executing the life-expectancy function to estimate a life expectancy of the secondary battery by assigning the accumulating portion resistance determined by the accumulating portion resistance determining unit and the increase coefficient determined by the increase coefficient determining unit.   
     
     
         12 . The apparatus of  claim 7 , wherein the life-expectancy estimation unit determines a time when the secondary battery comes to the end of its operating life by using a time when the internal resistance determining unit received the current and voltage change values. 
     
     
         13 . A secondary battery life-expectancy estimation system for estimating a life expectancy of a secondary battery, comprising:
 a current/voltage detection unit attached to the secondary battery; and   a secondary battery life-expectancy estimation apparatus according to  claim 7 .   
     
     
         14 . The secondary battery life-expectancy estimation system of  claim 13 , wherein the current/voltage detection unit performs the processes for:
 receiving current and voltage change values measurement command from the secondary battery life-expectancy estimation unit; and measuring the current and voltage change values of the secondary battery and transmitting these values to the secondary battery life-expectancy estimation unit.   
     
     
         15 . A secondary battery life-expectancy estimation system for estimating a life expectancy of a secondary battery, comprising:
 an internal resistance determining means for determining an internal resistance of the secondary battery from variations in current and voltage;   an accumulating portion resistance determining means for determining an accumulating portion resistance of the secondary battery from the internal resistance;   an increase coefficient determining means for determining an increase coefficient of said accumulating portion resistance from condition parameters including an operating voltage and a surrounding temperature of the secondary battery; and   a life expectancy estimating means for estimating a life expectancy of the secondary battery from the accumulating portion resistance and the increase coefficient.   
     
     
         16 . The secondary battery life-expectancy estimation system of  claim 15 , wherein said life expectancy estimating means further comprising:
 a storage means for prestoring determining function for estimate a life expectancy of the secondary battery, and a life expectancy calculating means for executing said determining function.   
     
     
         17 . The secondary battery life-expectancy estimation system of  claim 15 , wherein said internal resistance determining means performs processes for:
 accepting a life-expectancy estimation start command for instructing start of life expectancy estimation;   receiving current and voltage change values from a current/voltage detection;   and determining an internal resistance from the held current and voltage change values.   
     
     
         18 . The secondary battery life-expectancy estimation system of  claim 17 , wherein said accumulating portion resistance determining means performs the processes for:
 reading the accumulating portion resistance determining function from a storage unit; and   determining an accumulating portion resistance by assigning said internal resistance to said accumulating portion resistance determining function.   
     
     
         19 . The secondary battery life-expectancy estimation system of  claim 15 , wherein said increase coefficient determining means performs the processes for:
 reading the accumulating portion resistance increase coefficient determining function from a storage unit; and   determining an accumulating portion resistance increase coefficient by assigning operating condition parameters to the read accumulating portion resistance increase coefficient determining function.   
     
     
         20 . The secondary battery life-expectancy estimation system of  claim 15 , wherein said life expectancy estimating means performs the processes for:
 reading the life-expectancy estimation function from a storage unit;   estimating a life expectancy by assigning the accumulating portion resistance and the increase coefficient to the read life-expectancy estimation function.